(Delphi DLL) Decrypt S/MIME and Verify S/MIME Signatures

Delphi DLL example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Cert, Mime;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
mime: HCkMime;
isEncrypted: Boolean;
isSigned: Boolean;
signerCert: HCkCert;
decryptCert: HCkCert;

begin
success := False;

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

mime := CkMime_Create();

// Load an S/MIME message from a file:
success := CkMime_LoadMimeFile(mime,'signedMime.txt');
if (success = False) then
  begin
    Memo1.Lines.Add(CkMime__lastErrorText(mime));
    Exit;
  end;

// The ContainsEncryptedParts/ContainsSignedParts methods
// can be called to determine if the MIME is encrypted and/or signed:
isEncrypted := CkMime_ContainsEncryptedParts(mime);
isSigned := CkMime_ContainsSignedParts(mime);

// We don't want the "unwrap extras".  You'll see what those
// are in a few moments...
CkMime_putUnwrapExtras(mime,False);

// To verify the signature, call UnwrapSecurity.  This will
// verify the signature(s) and decrypt the S/MIME and restore
// the MIME to the unsigned/unencrypted state.
// The results of what was found are present in the MIME object's
// properties, as well as extra header fields that are added
// to the unwrapped MIME.
success := CkMime_UnwrapSecurity(mime);
if (success <> True) then
  begin
    // UnwrapSecurity returns True if all signatures were
    // verified and all parts decrypted.
    Memo1.Lines.Add(CkMime__lastErrorText(mime));
    Exit;
  end;

// The mime.UnwrapExtras property controls whether or not
// these additional fields are added to the unwrapped MIME:
// 
// X-NumPartsSigned: 1
// X-SignaturesValid: yes
// X-NumPartsEncrypted: 1
// X-Decrypted: no
// 
// The X-NumPartsSigned/X-SignaturesValid headers are added
// if the MIME was signed.  
// 
// The X-NumPartsEncrypted/X-Decrypted headers are added
// if the MIME was encrypted.
// 

// If the MIME was signed, get the certificate used for signing.
if (isSigned = True) then
  begin
    signerCert := CkCert_Create();

    // The NumSignerCerts property indicates how many certificates
    // were used for signing.  This example will assume the value is 1.
    // To get the 1st signer cert, call LastSignerCert with an index of 0:
    success := CkMime_LastSignerCert(mime,0,signerCert);
    if (success = True) then
      begin
        Memo1.Lines.Add('**** Signer Cert: ' + CkCert__subjectCN(signerCert));
      end;
  end;

// If the MIME was encrypted, get the certificate used for decryption
if (isEncrypted = True) then
  begin
    // The NumDecryptCerts property indicates how many certificates
    // were used for decrypting.  This example will assume the value is 1.
    // To get the 1st decrypt cert, call LastDecryptCert with an index of 0:
    decryptCert := CkCert_Create();
    success := CkMime_LastDecryptCert(mime,0,decryptCert);
    if (success = True) then
      begin
        Memo1.Lines.Add('**** Decrypt Cert: ' + CkCert__subjectCN(decryptCert));
      end;
  end;

// Display the unwrapped MIME:
Memo1.Lines.Add(CkMime__getMime(mime));

// Save the unwrapped MIME to a file:
success := CkMime_SaveMime(mime,'unwrappedMime.txt');

CkMime_Dispose(mime);
    CkCert_Dispose(signerCert);
    CkCert_Dispose(decryptCert);

end;